Power generation performance of fuel cell is strongly depended on net surface area of catalyst contained in a catalytic electrode. When the surface area is increased, the current density at electrical generation is increased to improve the output voltage. Downsizing of catalyst in the form of several nanometer particles is an effective method to increase the surface area of the catalyst per unit mass. Thus, nanoparticles of metal or alloy with a diameter of about 5 nm have usually been used as catalyst nanoparticles.
On the other hand, there was a problem of reducing the total surface area of the catalyst due to mutual aggregation of the catalyst nanoparticles during electrical generation by fuel cell. In order to suppress such aggregation by dispersing the catalyst nanoparticles into the catalytic electrode, the catalytic electrode with large surface area, comprising acetylene black with a diameter of 30-100 nm as a main constitutive element, has generally been used. Since the catalyst nanoparticles were produced on the acetylene black according to reduction-precipitation method or the like, they were physically adsorbed on the catalytic electrode surface. However, due to a week interaction between the catalytic electrode surface and the catalyst nanoparticles, this method is not capable of preventing the aggregation of smaller catalyst nanoparticles especially with a diameter of 1-3 nm. Large surface area of the catalyst nanoparticles fails to be kept during electrical generation. Excellent power generation performance which appeared at the earlier stage therefore rapidly disappears.
In order to solve this problem, proposed were a method for immobilizing platinum nanoparticles by degrading carbon monoxide or hydrocarbons at the surface of the platinum nanoparticles which serve as catalyst nanoparticles and adsorbing carbon to the site adjacent thereto (Patent Publication 1) and a method for implanting platinum into the carbon nanoparticles by simultaneously evaporating carbon and platinum with arc discharge (Patent Publication 2). Also there was a method for introducing chemical bonding force based on molecular cross-linked structure or the like at an interface between the catalyst nanoparticles and the carbon nanoparticles such as acetylene black and immobilizing those (Patent Publication 3).    Patent Publication 1: Japanese Patent Laid-Open Publication No. Sho 54-82394    Patent Publication 2: Japanese Patent Laid-Open Publication No. 2006-140017    Patent Publication 3: Japanese Patent Laid-Open Publication No. 2004-207228    Patent Publication 4: Japanese Patent Laid-Open Publication No. 2005-087864    Patent Publication 5: Japanese Patent Laid-Open Publication No. 2005-129369    Patent Publication 6: Japanese Patent Laid-Open Publication No. 2006-156366